#define _CRT_SECURE_NO_WARNINGS	

#include<stdio.h>

int main()
{
    int n;
    scanf("%d", &n);
    double sum = 0;
    int flag = 1;
    for (double i = 1; i <= (double)n; i++)
    {
        sum += flag * (i) / (2 * i - 1);
        flag = -flag;
    }
    printf("%.3f", sum);
}